The present invention is concerned with a method and apparatus for monitoring the progress and composition of a cloud of aerosol particles that had been released previously into the atmosphere. By xe2x80x9cprogressxe2x80x9d is meant position and concentration relative to a region for which said aerosol cloud may pose a health hazard.
Expressly incorporated herein are the following patents concerning means and techniques by which such aerosol constituents of the cloud may be classified and/or identified:
4,548,500xe2x80x94xe2x80x9cProcess and Apparatus for Identifying or Characterizing Small Particles.xe2x80x9d (Oct. 22, 1985).
4,693,602xe2x80x94xe2x80x9cMethod and Apparatus for Measuring the Light Scattering Properties of Small Particles.xe2x80x9d (Sep. 15, 1987).
4,710,025xe2x80x94xe2x80x9cProcess for Characterizing Suspensions of Small Particles.xe2x80x9d (Dec. 1, 1987).
Most of the aerosol particles present in the Earth""s atmosphere pose little or no health hazard. Even the occasional dangerous aerosol particle is of negligible importance because its concentration is so low However, when pathologically hazardous aerosol particles occur in great numbers, their potential to cause illness or injury increases dramatically The presence of high concentrations of such aerosol particles can occur naturally or from man made sources. Volcanic eruptions are examples of the former while accidental chemical plant releases and refinery plant explosions are representative of the later.
Other natural releases of potentially dangerous aerosols include those occurring during the rapid formations of photochemical smogs, often initiated by manmade contributions such as automobile exhaust products. The natural releases of fungal spores, such as Coccidiodes immitis, the causative agents of coccidioses, under the occasional environmental conditions needed to promote the rapid growth and maturation of the parent fungi, can have devastating effects on the health of those affected. Finally, there is a large range of potentially lethal aerosols that might be released by terrorist or military groups intent on inflicting great numbers of casualties. These include aerosols of both biological and chemical origin and their release is generally expected to be surreptitious.
When dangerous aerosol particulate clouds occur within or adjacent to populated areas, it is desirable to provide an early warning for the inhabitants that might be affected were they to inhale such aerosols. Such warnings can result in a dramatic reduction of casualties in spite of the possible unpredictable collateral responses, such as civil unrest due to fear or panic, by the endangered population. It has often been reasoned that by the time such aerosol threats are detected and identified, it is too late to issue a warning to the potentially affected population. This is not generally true.
Aerosol intrusions often occur as dispersals in the form of clouds released above the ground. For example, volcanic eruptions generally send huge quantities of material into the upper atmosphere from which the aerosol particles fall back to the earth and only affect the local populations once they reach near ground levels. In ambient air, a particle of radius 10xe2x88x926 m=1 xcexcm and density of 1 gm/cm3 would require almost 3 hours to fall just one meter. Thus with a suitably deployed warning system, the threat posed by such aerosols will be ascertained long before they reach altitudes or locations where their presence might cause injury.
There are many types of aerosols that are hariless. Obvious examples are water droplets or even fine ice mists. It is important that any viable warning system be able to differentiate between potentially dangerous aerosols and the more common harmless varieties.
The means by which aerosol threats to a local population be recognized is an important object of this invention. Obviously, for volcanic eruptions or chemical plant explosions or similar aerosol intrusions, the source and location of the resultant aerosol cloud is easily noted and tracking is often straightforward, except perhaps at night if visual means are used. This type of daylight tracking is generally passive and based on the observation of the effect of such intrusive clouds upon background illumination. Knowing the source of the cloud means that its composition is also known, at least initially. Instrumentation may be brought into the affected regions for purposes of local compositional monitoring that, eventually, forms the basis for evacuation planning if needed. Additionally, once a potentially threatening aerosol cloud has been detected, its monitoring may be achieved to some degree by optical or radio wave probing of the cloud using laser or radio sources at a safe distance from the threat.
A popular concept for providing warning of an aerosol threat is based on a traditional RADAR approach using laser produced radiation to probe the cloud threat at a distance. NASA had applied such techniques in their extensive measurement programs of 1989 through 1990 as a means for the profiling of aerosol and cloud backscatter, Doppler wind measurements, and the measurement of atmospheric trace species. Despite exceedingly large Federal expenditures in this area, the technique is not expected to yield any practical optical signals capable of permitting cloud composition to be deduced. Nevertheless, for clouds of known origin, composition may be deduced based on such a priori information. Ulich et al. in their U.S. Pat. No. 5,257,085 discuss many elements and variations of this technique for probing the physical properties of distant scenes by use of both active and passive interrogations.
The LIDAR (light detection and ranging) technique has various faults including requirements for an unimpeded view of the aerosol, i. e. without intervening particulates, atmospheric interferences, or opaque structures. Inferring aerosol concentrations from such LIDAR measurements of unknown particles is unlikely. Mixed aerosol compositions as well as size distributions that are changing in time illustrate further shortcomings of the concept. Esproles, in his U.S. Pat. No. 5,345,168, has explored some novel means for improving the information content in the returned LIDAR signal. Min et al. in their U.S. Pat. No. 5,102,218 discuss LIDAR measurements at very short ranges, generally less than 30 meters, for extracting target signatures from mixtures of target components and naturally occurring aerosol particles. The referenced patent""s detailed description includes many references to the target aerosol discrimination techniques used for so-called active optical proximity sensors together with extensive discussion of the then-current state-of-the-art.
Stewart et al. in their U.S. Pat. No. 4,687,337 discuss the need to deduce the extinction coefficients of aerosol particles by means of instrumentation taken to the various sites to be studied. Such so-called point source or in situ measurements are contrasted in their patent to the conventional LIDAR measurements. However, bringing instrumentation and personnel into regions thought to contain dangerous aerosol particles is usually avoided. For this reason, remote-sensing techniques for probing suspected targets have always been considered preferable. Carrieri in his U.S. Pat. No. 5,241,179 discusses this requirement in greater detail explaining the research programs of the U. S. Army Research, Development, and Engineering Center from the 1960s. The objective of these programs was the development of remote sensors xe2x80x9c. . . for detecting threat chemical and biological agents in vapor cloud, aerosol, rain, and . . . xe2x80x9d as surface contaminants. A need for passive spectroscopic techniques was recognized in the early 1970s. Such techniques would collect and process radiance from natural or preexisting sources.
Advanced development on a remote chemical agent detection unit began in 1979. As of the filing of the Carrieri patent in late 1992, the differential scattering/differential absorption LIDAR devices, referred to simply as DISC/DIAL devices, were said to show the most promise and were considered the most technologically advanced vapor detection and range resolution systems currently in operation. Carrieri""s invention purported to extend these capabilities by means of a related standoff detection technology that could sense contaminants on/within terrestrial and manufactured surfaces using their infrared absorption/emission signatures permitting, thereby, personnel xe2x80x9c. . . to protect themselves and take appropriate action to decontaminate, or avoid contaminated areas altogether.xe2x80x9d These concepts still represented a far cry from the initial objectives for the remote characterization of aerosol particles and associated biological agents. There can be no doubt, reading these reports and the associated instrumentation descriptions, that ultimately some form of in situ detection and analysis would be needed.
Muran et al. hoped to address the need for in situ monitoring by means of their invention filed in 1998 and issued as U.S. Pat. No. 5,898,373. The method disclosed provides for the seeding of the regions to be interrogated at some future time with xe2x80x9c. . . sticky polymeric particlesxe2x80x9d that would adhere to the various local surfaces for long periods of time. Using spectrophotometer equipped airborne vehicles, the reaction of these specially prepared particles with dangerous chemicals or particles would produce characteristic emissions capable of detection by the airborne instrumentation. Alternatively, the region seeded with the sticky particles could be scanned from above using active laser systems to induce excitation emissions from the materials/particles xe2x80x9ctrappedxe2x80x9d by or adhering to the sticky particles. The sticky particles would be designed to incorporate suitable chemicals that would react with the target agents resulting in a unique photometric signature of the selected target candidates. The ability of these particles to be observed at the moment of their deployment could be considered fortuitous, at best, since each threat must have to have been anticipated by the appropriate deployment/seeding of a unique detector particle
Much Federal finding has been directed during the past 50 years to problems associated with the protection of military personnel from aerosol threats, usually in the form of biological and chemical weapons. Small portable field instruments that would be able to identify small samples with great speed have received considerable support. Additionally, the hope to develop xe2x80x9c. . . revolutionary point-detection technologies . . . that [include] detection devices [that] can be small (hand-held) instruments for individual soldier use . . . xe2x80x9d has long been sought by the Government for protection of military personnel. The quotation referenced above is from a late 1999 request for proposals by the Defense Advanced Research Projects Agency (DARPA) in which they delineate their so-called xe2x80x9cwish list.xe2x80x9d Although the concept of networking such devices is suggested, portability in the field is stressed.
Unfortunately, the DARPA emphasis, discussed above, falls short of a practical approach in several regards: First, is the lack of a warning system for purposes of alerting the civilian population of an impending threat. The first detection with such DARPA devices would occur when the individual carrying the device enters the field or is enveloped in the threat cloud. There is no attempt to develop an early warning system. Next, this particular procurement devotes extraordinary attention to the need of avoiding false positive alarms despite the fact that the mere presence of a biological aerosol itself is cause for immediate concern and alarm. Naturally occurring biological aerosols are extremely rare events.
Key to any warning system is the ability to detect the aerosol threat as soon as possible after it has been released. Once an aerosol threat has been released, the local concentrations of the offending particles are extremely high. For example, it has been estimated recently, following the analyses of the Russian anthrax accident at their Sverdlovsk facility, that about 10 viable spores of B. anthracis are required in the lungs of a healthy individual to cause disease. This would require ambient concentrations of the order of tens of thousands per liter of air. To achieve such concentrations, the aerosol concentrations near the release zone would require the presence of at least 106 to 107 per liter of air. Accordingly, near the release point, classification/identification becomes a much-simplified task because of the expected similarity of each member of the aerosol cloud ensemble. Finding a suitable signal becomes far simpler if detection is prompt and close to the release: an objective of the present invention. In such a huge collection of positively identified aerosol particles, the probability of misclassifying the entire ensemble, and thus the detected event itself, becomes vanishingly small. It is a major objective of the present invention to focus xe2x80x9con the forest,xe2x80x9d so to speak, rather than a particular xe2x80x9ctree.xe2x80x9d
Additional emphasis of the DARPA procurement, which is typical of those issued by the Federal Government during the prior 30 years, is placed upon the need to differentiate between live and dead biological particles in the threat aerosol cloud. The belief that confirmation of the fact that because a threatening aerosol contains an overwhelming quantity of dead microorganisms, there are no remaining dangers associated with the trace viable cells cannot be considered a valid analysis of such a threat. The detection of the presence of potential pathogens, irrespective of their viability, is an essential element of any early warning system.
Threats associated with chemical agents are addressed also by various Federal procurement activities. One of the more interesting is the Shipboard Automatic Liquid Agent Detector (SALAD) program whose specification and related solicitations have long been in progress. xe2x80x9c. . . The SALAD acquisition program has been initiated to provide the Navy with the capability to automatically detect liquid chemical warfare agents. This acquisition program has been underway for approximately five years during which the Government has developed and produced a prototype SALAD that has been analyzed and tested to confirm its potential to meet Navy operational requirements . . . xe2x80x9d Later, within the specifications, it is stated xe2x80x9c. . . The SALAD shall automatically detect liquid nerve (G- and V-series) and blister (H- and L-series) agents at the concentrations and droplet sizes as follows:xe2x80x94concentration: 2.0 mg/m2 and higher-droplet size: median mass diameter of 500 micrometers and larger {Objectivexe2x88x92200 micrometers and larger} . . . xe2x80x9d What is particularly striking about this activity is the enormous size associated with the median size: 500 xcexcm. At this size in ambient air, the particle will fall I meter in about 22 seconds. The detection system has 60 seconds to make an identification of the agent and issue a warning within which time the particle would have fallen almost 3 meters. Detection issues are complicated farther by the ship""s motion as well as ambient wind effects on moving the agents. Associated with such large particles are expected to be smaller particles that may well be undergoing evaporation. It is this latter fraction of a deployed chemical agent aerosol that would be most usefully detected since the aerosol""s associated size distribution would be changing in time. It is a further objective of the present invention to monitor the size distribution and its changes with time as a means for detection of such agents. Natural aerosols comprised of water particles would exhibit similar behavior except for a very important and easily detected difference: the refractive index of water droplets is expected to be about 1.33 in contrast to that of a typical chemical agent. The present invention will extract the refractive index of selected aerosol particles as required from their recorded light scattering characteristics.
It is an object of the present invention to provide an explicit means to detect and monitor the composition of a potentially threatening aerosol cloud arriving at remote locations by remotely positioned detector means. Such detectors, called xe2x80x9cdetector stations,xe2x80x9d are capable of performing a set of scattered light measurements by which the target aerosol particles are well classified and/or identified, one-at-a-time, at each locale where they are detected. Each detector station transmits its collected and processed information by telemetric means to a central station that is responsible for further processing of the received data. Important among the latter processing activities is the prediction of the movement of all elements of the aerosol cloud.
Another objective of this invention is to process further the reduced data received by transmission means from each deployed detector station to permit prediction of arrival time and threat danger to sites not yet exposed to said aerosol cloud. A means by which air mass movement could be followed is described in U.S. Statutory Invention Registration # H111 issued Aug. 5, 1986 to Barditch et al. Their tracking technique seems of little practical consequence since they must seed the air mass to be monitored at one location with Bacillus thurengiensis spores and then culture a sample of air collected at a second location. The subsequent growth on a specially prepared culture plate of the seed spores confirms the origin of the sampled air and the numbers recovered a measure of the diffusion of the seeded sample during its journey. This method is inapplicable as a warning system and requires the a priori detection and location of the aerosol threat. Sometimes, should the aerosol threat be detected or noticed and if it is known to contain spores or other culturable organisms, such sampling may provide a historical record of the threat, but no warning. Interestingly, and as a consequence of the present inventive method, the bacterial spore seeding implementation of Barditch et al. could easily be replaced thereby using polystyrene latex spheres of nominal diameter 1 xcexcm. Since such particles are readily detected in real time with an element of the present invention, results can be almost instantaneous since no time- and labor-consuming culturing would be required.
Another objective of the invention is to provide rational central station decisions, based upon analyses of all data collected from the set of deployed detector stations, to provide an alarm and/or warning of the expected arrival time of the dangerous aerosol cloud and its probable composition and suggested means for protection of the soon-to-be-exposed populations. This alarm and warning is prepared for each locale on an individually calculated basis. Thus one region might be given a ten-minute warning whereas another simultaneously might receive a two-hour warning. Each such report to each specified locale is updated in a timely manner and communicated to each potentially affected locale to insure maximal warning for the threatened population.
A further objective of the invention is to use the central station to regulate data collection and analysis rates at each detector station, collectively or individually, by telemetry means.
There are many different means for characterizing aerosol particles at a fixed location. For example, Cole in his U.S. Pat. No. 5,296,910 describes the use of multiple force fields combined with Doppler velocimetry to obtain particle density, diameter, electric charge, magnetic moment, and other physical attributes of individual particles. Gerber in his U.S. Pat. No. 5,315,115 describes optical means of determining particulate integrated properties that could then be used to classify an aerosol in terms of its integrated volume concentration, integrated surface area concentration and aerosol extinction coefficient in the infrared spectral region. The text xe2x80x9cModern methods of particle size analysisxe2x80x9d edited by Howard Barth (Wiley-Interscience, New York 1984) discloses a large number of techniques by which the aerosol particle sizes may be determined. Theodore Provder has edited several collections of papers for the American Chemical Society Symposium Series on the analysis and characterization of particles and particle size distributions under the title xe2x80x9cParticle size distributions I, II, and IIIxe2x80x9d in 1987, 1992, and 1998. There are literally hundreds of texts and thousands of scientific articles on related topics of particle characterization. There is, however, one technique with the greatest breath of application for aerosol particle characterization.
The most powerful technique for differentiating and characterizing individual aerosol particles is by means of light scattering. In their broadest sense, light scattering measurements are performed using a collimated monochromatic light beam through which the particles pass, generally one-at-a-time. During its transit through the beam, a particle scatters some of the light incident upon it. This scattered light is then collected by means of collimated detectors positioned at discrete scattering angles with respect to the direction of the incident light beam. Each detector may be fitted with various optical elements including polarizing analyzers, interference filters, electrooptical shutters, neutral density filters, waveplates, and other optical elements. Even in its simplest implementation, with all detectors lying in a plane and no analyzer at any detector, Wyatt and his co-workers have demonstrated the powerful characterization capabilities of the technique including the following:
For determining the refractive index and size of simple, homogeneous polystyrene latex particles
xe2x80x9cMeasurement of the Lorenz-Mie Scattering of a Single Particle: Polystyrene Latex,xe2x80x9d with D. T. Phillips and R. M. Berkman, J. of Colloid and Interface Science 34, 159 (1970):
For the study of bacterial spores
xe2x80x9cDielectric Structure of Spores from Differential Light Scattering,xe2x80x9d Spores V, American Society for Nicrobiology, (1971);
xe2x80x9cObservations on the Structure of Spores,xe2x80x9d J. Applied Bacteriology 37, 48 (1975);
For the detection and characterization of photochemical smog particles
xe2x80x9cSingle Particle Light Scattering Measurement: Photo-Chemical Aerosols and Atmospheric Particulates,xe2x80x9d with D. T. Phillips, Applied Optics 11, 2082 (1972);
For differentiating aerosolized bacterial cells
xe2x80x9cStructure of Single Bacteria from Light Scattering,xe2x80x9d with D. T. Phillips, J. Theor. Biol. 37, 493 (1972);
For measuring the accretion of acid-like coatings on aerosol particles generated by power plants
xe2x80x9cSome Chemical, Physical and Optical Properties of Fly Ash Particles,xe2x80x9d Applied Optics 14, 975 (1980);
The detector system described in U.S. Pat. No. 4,693,602 by Wyatt et al., as well as in the paper:
xe2x80x9cAerosol Particle Analyzer,xe2x80x9d with Y. J. Chang, C. Jackson, R. G. Parker, D. T. Phillips, S. D. Phillips, J. R. Bottiger and K. L. Schehrer, Applied Optics 27, 217 (1988),
represents an early version of a more general detector incorporating out-of-plane measurements as well as depolarization analyzers. This earlier device as disclosed and implemented was very large, requiring an argon-ion or HeCd laser as an illumination source and individual photomultiplier detectors connected to a read head by means of optical fibers. Accordingly, it had a very high power consumption that made it difficult to operate on battery supplies for extended periods of time. The photomultiplier power supplies and assorted computer and aerosol handling systems added further bulk and cost to the analyzer making it impractical for any type of field deployment.
In order to monitor successfully potentially dangerous aerosol threats and differentiate them from harmless constituents, a large number of individual light scattering detector stations must be placed strategically around and throughout the region to be protected. Although the concept of a xe2x80x9cpoint sourcexe2x80x9d detector, i. e. one that is localized and restricted in its range of detection, has been recognized for many years, the concept of linking such detectors cooperatively in a network and providing individual detectors the means to function filly and independently in classifying the local aerosols it may sample has not been considered previously and represents a further objective of this invention.
Networked detectors have been used extensively for telecommunications purposes and similar techniques of lid localized detector units have been used frequently to provide fire and intruder protection for buildings and similar regions. Such so-called wireless warning systems employ a variety of signal processing techniques to insure high reliability. For example, Sanderford et al. in their U.S. Pat. No. 5,987,058 employ a spread spectrum technology with high reliability for the continuous monitoring of a building. Sheffer et al. in their U.S. Pat. No. 5,568,53 5 describe explicitly a cellular alarm unit that includes cellular phone functions permitting cellular connections to remote monitoring stations. The remote monitoring stations detect an emergency condition by means of sensors that preferably include fire sensors, perimeter sensors for detecting opening of doors or windows, for example, and a panic switch for activation by an individual within the enclosed area in the event of a medical or other emergency. The Sheffer et al. system is intended to circumvent more conventional hard-wired systems that are easily defeated by severing the traditional telephone wiring. There are many other types of alarm systems that provide for efficient, cost-effective and reliable cellular-type radio/telephone communication system included within an alarm system to provide wireless communication such as described by Smith et al. in their U.S. Pat. No. 4,993,059.
All of the aforementioned alarm systems that make use of a network of cellular or other wireless intercommunications means are based on sensors intended to detect and then warn of a class of easily monitored phenomena. Most important among these are fire and smoke detection, intruder presence, physical parameters such a temperature and humidity, panic alarms, television monitoring stations, radiation detection, etc. As will be evident from the detailed description of the present invention, the sensors used therein are both distinct and uniquely different from sensors of these types in the following ways: the sensors provide for data collection and real-time processing and analysis; the sensors incorporate a variety of electrooptical elements as well as a fully functional microprocessor; they can be reprogrammed, the sensors include means for sample handling.
Each station must be capable of processing the data it collects and telemetering the results to a central station that would collect such results from all stations for subsequent analysis and make decisions concerning alarms or other warnings. Despite the existence of a wide range of analytical tools for the counting, sizing and classifying aerosol particles, there has been no attempt to integrate some of these tools with a means for appraising the threat of an aerosol intrusion and alerting the targeted population of the need to protect itself. The present invention discloses a straightforward means by which this may be achieved.
The invention disclosed here describes a means, comprised of an array of light scattering detector stations and their ancillary electronic and physical infrastructure, by which communities, buildings, compounds, military bases, airports, embassies, parks and other selected regions may be warned of the presence of an impending aerosol threat. Key to the successful operation of such a system are detector stations capable of preparing ambient air samples for measurement, measuring and classifying aerosol particles therein one-at-a-time using multiangle light scattering over a broad range of discrete scattering angles, identifying specific threat subclasses from the data so-collected and analyzed within the collected aerosol sample, counting relative numbers of such subclasses, monitoring physical changes that may be occurring throughout the analysis period, and reporting all processed data via integrated telecomnunications links to a central control station.
Each light scattering detector station includes a scattering chamber traversed by a fine laser beam, together with the capability to: dilute the sampled aerosol stream so that only a single particle is in the beam at any moment; make light scattering measurements on each transiting particle over a broad range of discrete scattering angles using detectors that may incorporate polarization and fluorescence analyzers; and, process the data collected identifying, thereby, the type and class of each aerosol particle measured. Data processing and classification are achieved using an integrated microprocessor system that contains random access memory and read only memory incorporating the preprogrammed software required for particle classification. In addition, each such station has a compact transmitter similar in concept to the GHz transmitters used by conventional cellular telephones.
Each detector station, which has been sited previously to form a component of a multi-detector network spanning the region to be monitored, is connected via a telecommunications link to a central station The central station receives and processes all data transmitted from the linked detector stations. On the basis of such processed data, the central station monitors the aerosol cloud""s position and composition, evaluates all potential threats to the region being monitored, commands specific detector stations as required to change or modify such detectors"" specific collection rates and processing, and issues alarms and/or near real-time warnings to subregions of any potential problems expected from the aerosol cloud.